I have to run a statistical analysis on a data set I obtained
recently.

This is my problem:

An individual was instructed to look at three possible computer
screens and we measured how many times they fixated within a
particular area.

Two screens had an area of 4 units.
The third screen had an area of 5 units.

The two screens having an area of 4 units obtained 15 fixations each
while the screen of 5 units obtained 20 fixations.

Prior to running any statistical analysis to see if there is a
significant difference between screen type and the number of
fixations, I have to correct for the differences due to screen size
(as a larger screen area would naturally result in more fixations).

Any help in how to do this correction would be appreciated (I provided
arbitrary numbers as our data set is somewhat more complex, but if you
could help me with the numbers provided, I should be able to easily
adapt it to our data).